The multilayer ceramic capacitors are widely used in current electronic products, such as personal computer (PC), mobile phones, vehicle electronic devices, and etc. The structure of a multilayer ceramic capacitor includes a dielectric ceramic body and inner and outer electrodes. The dielectric ceramic body includes barium titanate (BaTiO3) as a primary component and some other various additives for forming the NPO, COG, Y5V, X7R, X8R, Z5U, etc. type of multilayer ceramic capacitors. The applications of these multilayer ceramic capacitors are also different basing on their electrical property, while the property is mainly decided by the dielectric ceramic body.
The multilayer ceramic capacitors satisfying the X8R characteristics of the EIA standard are widely used in the microelectronic devices operating at a large temperature range due to the good stability of the dielectric temperature from −55 to 150° C. and ΔC/C≦15%. However, for some vehicle electronic devices, such as the electronic engine controlling units (ECU), the anti-lock braking systems (ABS), the programmed fuel injection system (PGM FI), and etc., it is required to operate in more critical conditions. Therefore, it is needed for the multilayer ceramic capacitors to have smooth and large operating temperature range in the case that they are applied in such critical conditions. With the advance of technology and basing on safety consideration, development of the dielectric material for satisfying the X9R characteristics (−55 to 200° C. and ΔC/C≦15%) regulated by the Association of Electrical Industry, or satisfying the operation with more large temperature range, becomes the inevitable demand.
In the current development of the multilayer ceramic capacitors satisfying the X8R characteristics, barium titanate (BaTiO3) is usually applied to be a primal component due to its higher dielectric constant. However, the crystal structure of barium titanate will transfer to the paraelectric cubic phase from the ferroelectric tetragonal phase and a dielectric peak will appear at the Curie temperature (Tc), which will affect the dielectric temperature stability. Because the Curie temperature of barium titanate is about 130° C., it is necessary for the dielectric ceramic material mainly formed of barium titanate to add various Curie shifter, grain growth inhibitor and sintering aids, etc., for promoting the temperature stability of the dielectric material.
The published U.S. Pat. No. 7,821,770 discloses a multilayer ceramic capacitor satisfying the X8R characteristics and having a high stability in the high temperature environments. The components include 100 mol of barium titanate (BaTiO3), 0.4 to 3.0 mol of magnesium oxide (MgO), 6.0 to 16.5 mol of rare earth oxide (ReO3/2), 3 to 5 mol of silicon oxide (SiO2) and 0.05 to 0.4 mol of metal oxide (MOx), wherein the rare earth oxide can also be selected form the oxide of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Y; and the metal oxide can be selected from the oxide of V, Cr or Mn.
Another published U.S. Pat. No. 7,541,306 also discloses a multilayer ceramic capacitor satisfying the X8R characteristics. The dielectric ceramic material includes the barium titanate base material doped with other metal oxides such as BaO, Y2O3, ZrO2, SiO2, MgO, MnO, MoO3, CaO, Lu2O3, Yb2O3, or WO3.
The published U.S. Pat. No. 7,751,178 discloses a dielectric ceramic material for promoting the stability of the multilayer ceramic capacitors to satisfy the X8R characteristics (−55 to 150° C. and ΔC/C≦15%). The dielectric material includes a perovskite type compound as a primary component. The chemical regulation of the compound is (Ba1-x-yCaxSny)m(Ti1-zZrz)O3, wherein 0.1≦x≦0.2, 0.02≦y≦0.2, 0≦z≦0.05, 0.99≦m≦1.015. The dielectric material also includes the accessory component of rare earth elements. Each 100 mole of the perovskite type compound is added with 0.5 to 20 mole of the accessory component, and the accessory component is selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y.
However, with the advance of the technical development, the demand to the material is also increased. Therefore, if the multilayer ceramic capacitors can be operated in a wide temperature range, the industry usage thereof will be further promoted.